THE PROBLEM OF MITOGENETIC RAYS 925 



For all yeast experiments as conducted by the Gurwitsch school, a 

 standard beer wort is needed. This beer wort must have about "18 

 balling" sugar. If it has less, the proper amount of sugar must be added, 

 if more, the wort must be diluted. Recently Braunstein and Potozky 

 (33) have published a paper on the use of a synthetic medium, but it has 

 apparently been used only in one laboratory. The wort as it is generally 

 used is sterilized for 10 min. at 2 lb. pressure. After several days the 

 flocky precipitate is filtered off and the wort poured into test tubes. 



The yeast used is usually Saccharomyces ellipsoideus, a wine type or 

 Nadsonia yeast. Slant cultures are prepared with agar containing beer 

 wort of 6 to 10 balling instead of water. These agar slants are considered 

 best after incubation for 20 to 30 days at 25°C. These are the so-called 

 stock cultures. There are, in fact, two entirely different methods of 

 using the yeast as a detector: (a) The agar method. (6) The liquid-yeast 

 method. For the agar or "solid" culture method Petri dishes are 

 prepared with an even layer of fairly solid agar. A finely divided sus- 

 pension of the stock culture is permitted to settle on the agar surface. 

 The supernatant is then poured off, the Petri dish is kept for 8 to 10 hr. 

 at 16° to 18°C., and the agar layer is cut into small blocks, each with an 

 area of about 1.5 cm. and apparently with a uniform layer of yeast. 

 These small blocks are again cut so that one half is used for the detector 

 and the other for the control. It is important that the pieces used as 

 "detector" and "control" should be cut from neighboring sections. In 

 setting up the experiment, the detector is exposed to the sender behind 

 a thin plate of quartz. This quartz must have been previously tested 

 for its transmission of mitogenetic rays, and a test for the transmission of 

 short ultra-violet radiation is not considered sufficient! After exposure 

 the yeast blocks are incubated at 24° to 25°C. for 1.5 hr. Slides are 

 prepared by coating these with a thin layer of egg white. The yeast from 

 the block is distributed in a drop of distilled water and spread over the 

 slide. The slide is then allowed to dry and is fixed by moving it through 

 the flame; the slide is then stained with methylene blue, washed, and 

 dried. All slides are counted with 3^2 oil immersion, the only considera- 

 tion being that of determining the number of "mother cells" and of 

 "buds." 



The judging of whether one has a "mother" or a "bud" cell presents 

 one of the most important and most difficult steps in the whole agar- 

 yeast procedure. All cells which are attached, definitely round, and less 

 than one-fifth of the size of the cells to which they are attached are 

 counted as buds. If one encounters a doubtful case, the entire field is 

 supposed to be omitted. Special attention must be paid to counting cells 

 from all parts of the slide. At least 100 cells should be counted from 

 each slide, and if the first group of 500 differs very much from the second 

 in percentage of buds, another 500 should be counted. The number of 



